Wheel tractor scrapers are used to remove dirt for preparing a roadway for paving or for other road surface preparation. Such wheel tractor scrapers, as the Caterpillar.RTM. model 631E, are typically driven in the direction of the roadway and remove dirt to an appropriate depth, according to survey stakes positioned alongside the proposed roadway. The dirt is simultaneously removed as the ground below is leveled for providing an acceptably flat and smooth roadway. All standard highways and roads are desirably crowned in a parabolic shape, high in the middle and low along the edges of the roadway, primarily to facilitate drainage and also, to a lesser degree, to increase strength through the upwardly curved arch shape and to enhance safety by slanting each side of the roadway in opposite directions so that vehicles will have a tendency, although mostly imperceivable, to move away from the center. When a vehicle is not properly guided by an inattentive operator, it will drift to the side and away from oncoming traffic.
In order to provide the desirable parabolic crown or arch shape to the roadway, an existing wheel tractor scraper can be used to the surface only to the highest desired depth at the center of the road. Another piece of equipment, such as a road grader, must then be used to blade the dirt away from the edges on both sides of center. Graded dirt may also accumulate and may need to be removed from the roadway using one or two other pieces of equipment, such as the tractor wheel scraper or a front-end loader and a dump truck.
Prior U.S. Pat. No. 3,561,538 discloses an earth-moving machine with depth and cross-slope control. This machine provides for depth control using a pair of hydraulically operated rams that operate in parallel, i.e., both rams acting simultaneously up or down at the front of the main member so that the height of the blade is adjusted. The cross-slope is adjusted with a single hydraulically-operated ram operating against pivotable brackets which support one rear wheel by raising and lowering one of the rear wheels; the cross-grade is said to be adjustable. This prior device requires a specially constructed rear axle bracket and brace support that presents certain inherent suspension difficulty and reduced load-carrying capacity and has not been a widely accepted machine design.
Other prior tractor scrapers with material collection bowls, such as in U.S. Pat. No. 3,905,136 and U.S. Pat. No. 3,486,254 and U.S. Pat. No. 3,984,927 consistently describe tilting the front of the bowl downwardly or upwardly to adjust the depth of cut only with parallel actuation of hydraulic cylinders and rams or hydraulic actuators. In each of these prior devices, the front blade is tilted downward or upward, thereby adjusting the depth of the cut but not adjusting the cross-grade cutting angle.